1. Field of the Invention
The present invention relates to a pressure control valve for use with a variable displacement swash plate type compressor for regulating the amount of gas relief from a crank chamber to an intake chamber.
2. Description of the Related Art
There are known various pressure control valves of the type which include a valve element actuated by a pressure responsive member exposed to an intake pressure, and a solenoid for controlling the movement of the valve element in such a manner that the degree of communication between a crank chamber and an intake chamber of a compressor is adjusted according to the electric current intensity supplied to the solenoid. One example of such known pressure control valves includes, as shown here in FIG. 6 of the accompanying drawings, a valve case 28, a valve holder 29 firmly connected to one end of the valve case 28 and receiving therein a valve element 42 and a pressure responsive member 44 connected to the valve element 42. The valve holder 29 has an axial connecting hole 38 and a radial connecting hole 29 opening respectively to a crank chamber 4 and an intake chamber 27 of a compressor. The valve holder 38 includes a valve seat 40 formed at an inner end of the connecting hole 38 for engagement with the valve element 42. The pressure responsive member 44 is subjected to the pressure in the intake chamber 27. The valve element 42 is held in abutment with a stem 41 which is connected with an armature 32 of a solenoid 30 through a connecting pin 56 and a connecting rod 55. The armature 32, connecting rod 55 and connecting pin 56 extend centrally through an annular stator 33 of the solenoid 30. The armature 32 and the stator 33 have tapered confronting surfaces. When an electromagnetic coil 31 is energized, a magnetic force is produced between the armature 32 and the stator 33, tending to move the armature 32 rightward in this figure to thereby urge the valve element 42 toward the valve seat 40.
The pressure control valve of the foregoing construction is however disadvantageous in that the hysteresis between the intake pressure due to an increasing and a decreasing electric current supply to the electromagnetic coil is large, as indicated by broken lines shown in FIG. 4. The reproducibility of the pressure control valve is therefore very low.
The foregoing drawback is caused mainly by the abutment engagement between the valve element and the stem. With this abutment engagement, it is difficult to guide the valve element accurately in a direction parallel to the axis of the stem when the control valve is subjected to vibration. The valve element is hence likely to be seated unstably on the valve seat and also to produce a large amount of friction between itself and the valve seat. Another factor lowering the reproducibility is that the cumulative tolerance of the stem, valve element and valve holder and the mounting error of the pressure responsive member vary the distance between the armature and the stator and also alter the characteristics of the pressure responsive member.